Our goal is to determine the molecular functions of the myosin-I family of molecular motors. Myosin-Is comprise the largest unconventional myosin family found in humans (eight genes), and its large size and expression profile distinguish it as one of the most diverse. Myosin-Is physically link cell membranes to the underlying actin cytoskeleton where they play essential roles in powering membrane dynamics, membrane trafficking, and mechanical signal- transduction. Remarkably, the molecular functions of myosin-I are largely unknown, which is largely due to the lack of information about the basic biophysical properties of the proteins. Therefore, our goal is to provide the biochemical and biophysical foundation for understanding the molecular physiology of this important class of motors. We will use a combination of innovative biophysical techniques to define (1) the mechanics and dynamics of the membrane- myosin-I interface, (2) mechanical and force generating properties of myosin-I, and (3) biochemical and mechanical properties of myosin-I binding proteins.